Publication: Development of graphene nanoplatelets reinforced polyurethane coatings for enhanced hydrophobicity on steel surfaces
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Date
2025-08-07
Authors
Nur Anis Zulaikha binti Ahmmad Hussin
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Abstract
Polyurethane (PU), known for its flexibility, durability, and excellent adhesion to various substrates, is widely used as a protective coating material. Its performance can be further enhanced through the incorporation of functional additives and surface modification techniques. This research investigated the development of hydrophobic PU coatings on mild steel by evaluating different coating application methods, namely spin coating, Doctor Blade, and brushing to determine the most effective approach. Brushing was selected as the optimal technique due to its simplicity, cost-effectiveness, suitability for both smooth and irregular surfaces, and its ability to produce the highest water contact angle (WCA) among the methods tested, indicating superior hydrophobic performance. Using this method, PU coatings were modified with stearic acid (SA) at a 1:6 ratio to improve the distribution of particles, and graphene nanoplatelets (GNP) were incorporated at varying concentrations (0.25 wt.%, 0.5 wt.%, and 0.75 wt.%), with or without mesh patterning, to enhance the hydrophobicity, corrosion resistance, and surface roughness of the coatings. The PU/SA/GNP 0.75 wt.% coating with mesh achieved a maximum WCA of 121°, indicating enhanced hydrophobicity. Corrosion tests showed a significant reduction in corrosion rate to 3.12 × 10⁻⁶ mm/year, and surface roughness improved to 149.1 nm. Field Emission Scanning Electron Microscopy (FESEM) analysis confirmed that GNP reduced porosity and acted as an effective barrier. However, higher GNP concentrations caused particle agglomeration, reducing adhesion strength. Scratch testing showed failure at 15 N for PU/SA/GNP coatings vs. 18 N for PU, indicating reduced adhesion. Overall, the PU/SA/GNP 0.75 wt.% mesh coating offered the higher hydrophobicity, corrosion resistance, and surface roughness among all samples for mild steel protection.